The Royal Society has never suggested that the world should attempt large-scale climate geoengineering schemes as a "fix" for climate change (Leaders, October 29). None of these technologies will provide a "get out of jail free card", and they must not divert attention away from national or international efforts to reduce emissions of greenhouse gases.

However, the scale of the challenge we face in avoiding the worst impacts of climate change means that we need to look at all potential options and assess what their contributions might be.

This is why the Royal Society is launching a major study today, looking at whether any of these geoengineering technologies could be feasible or effective. It will also consider what environmental and social impacts they may have and any other possible unintended consequences. Some of the proposed schemes may prove to be as implausible as they seem, others may be ambitious but have potential. We must distinguish between the two and provide policymakers with sound, independent scientific advice, so they can make informed decisions based on fact, not fantasy. Martin Rees President, Royal Society

A gaping hole remains in the climate change bill despite the likely inclusion of emissions from aviation and shipping (Minister bows to calls on climate change bill, October 27). The government will still be able to buy "carbon credits" from abroad rather than taking action to reduce pollution at home. If the bill is to be more than an accounting fiddle, the Conservative party, in particular, must back our lobbying to plug this loophole. Ruth DaviesHead of climate change policy, RSPB

There is no credible evidence that algae photosynthesise faster, or are currently able to accumulate substantially more biomass, during a period of sustained growth than other green organisms (How algae could drive the future of biofuels, October 23). Intensive agriculture of any sort rarely uses less fossil fuel energy than the light energy that it conserves as biomass. Biofuels do not lead to any appreciable sparing of carbon dioxide emissions that could not be better accomplished by the most modest means of energy conservation, such as a small reduction of the legal speed limit on motorways. David WalkerEmeritus professor, University of Sheffield

Our political masters cannot be so ignorant or badly advised as to really believe that the widespread introduction of electric vehicles will cut greenhouse gas emissions (Report, October 28). At least one government scientific adviser must have pointed out that the electricity for charging batteries is currently produced mostly by coal- and gas-fired power stations. These have a lower efficiency than a modern internal combustion engine, plus account has to be taken of transmission, charging etc. Consequently, the amount of greenhouse gases produced would be likely to increase as a result of a move to electric propulsion.

It is not worth considering the large-scale introduction of (non-hybrid) electric vehicles until a major proportion of our electricity is generated from genuinely renewable sources. Advisers must also have pointed out that the new technology batteries use rare and valuable metals, such as nickel and lithium. Furthermore, the apparent cheapness of electric propulsion is illusory; it comes about simply because electricity does not currently attract the tax applied to other road fuels.Richard BarnardVisiting fellow, University of Hertfordshire

Your article repeats the mantra that the biggest obstacle to electric cars is the lack of a power infrastructure. There must be countless motorists, like me, who find the vast majority of their journeys are short hops. The only infrastructure I need is a socket on the garage wall. Moreover, I have just read that a new battery/capacitor combination has overcome the main disadvantage of lead-acid batteries by making it possible to recharge them without radically shortening their life. What stands in the way of the electric car is the failure of manufacturers to make small electric cars (the G-Wiz costs over £8,000 without VAT) that are in any way comparable to a typical small petrol car in terms of price and performance. Martyn StevensLeighton Buzzard, Bedfordshire